The rewards you offer your child do not have to be excessive either. Something as simple as an extra biscuit, or a few stickers can work. Make sure they are offered as a reward for staying dry – that means that AFTER your child has successfully used the potty, and stayed dry, he or she gets the reward. If you give your child a reward before the event, it is more like a bribe, and it is unlikely to be as effective!
You may also want to vary the motivation. Start off by offering a reward when your child sits on the potty, but move on to rewarding your child only when he or she uses the potty successfully.
Stick to rewards that offer immediate gratification too. Charts and long-term promises are unlikely to motivate your child to use the potty, because he or she will simply forget.